Repeatability of axial length measurement under the accommodation in pseudophakic patients using ultra-long scan depth OCT

Accommodation is the ability of human eye to change refractive power to see near target clearly.

This study was to investigate the repeatability of imaging axial length (AL) under the pilocarpine-induced accommodation in pseudophakic patients using ultra-long scan depth OCT (UL-OCT).

A prospective study was carried out.Twenty eyes of 12 subjects who received monofocal intraocular lens (IOL) implantation were incuded in the Eye Hospital of Wenzhou Medical University from October 2014 to January 2015.The patients aged from 56 to 84 years (mean: [69.9±7.6] years). A self-built UL-OCT, with center wave length 840 nm and the axial resolution 7 μm and scan depth 37.71 mm (in the air), was employed to image the whole eye picture through the pupil in relax and accommodative states.The images were analyzed by a self-developed software to acquire the central corneal thickness (CCT), anterior chamber depth (ACD), IOL thickness, vitreous length (VL) and AL.The parameters were repeatly measured for two times, and the percentage of coefficient of repeatability (COR) was calculated.The consistency between the two measurements was evaluated by Bland-Altman agreement test.

The average AL value was (23.241±0.882)mm, and the difference of repeated measurement values was (-0.008±0.026)mm under the relax state, without statistical difference between two measurements (P=0.283). The average AL value was (23.274±0.889)mm, and the difference of repeated measurement values was (0.002±0.028)mm under the accommodation state, without statistical difference between two measurement values (P=0.724). AL increased by (32±35)μm after the accommodation.The CORs were 0.222 and 0.240, and the COR percentages were 1.03% and 0.96% under the relax condition and accommodation condition, respectively.The Bland-Altman plots showed that the mean differences between the two repeated measurement values were close to zero in the relax condition and accommodation condition.

UL-OCT is a potential tool of obtaining AL of whole eye in pseudophakic eyes.